Fabric window coverings are often preferred by consumers for a number of their features. The features most often considered desirable are the softer appearance relative to traditional venetian blinds, the uniform appearance which they provide a window, and the insulating properties associated with cellular fabric shades.
U.S. Pat. No. 3,384,519 to Froget discloses one such attempt. The window covering disclosed therein consists of two cloth layers spaced apart by movable parallel blades having each of their marginal edges heat-welded to one of the movable cloth layers. With this window covering, relative movement of the two cloth layers in a direction perpendicular to the blades changes the angle of the blade and thus controls the amount of light admitted through the article. A number of undesirable features of the Froget window covering derive from the fact that it is constructed utilizing a heat-welding process. First, the process is limited to use of fabrics which may be heat welded, i.e. certain mutually compatible thermoplastic materials. Also heat-welding necessarily requires a melting of at least some of the fibers of the materials bonded. Because some of the fibers are melted, the fabric structures are weakened. Also it creates an uneven outer appearance along the heat-welds and producing unwanted crimps or creases in the materials, which can result in fatigue failure. Further, heat-welding is a relatively slow process which may require six or more seconds to create a bond over an extended length. This is too slow for high volume commercial production processes. Other drawback of the Froget window covering is the difficulty in achieving uniformly straight heat welded joints over an extended length.
In an earlier filed application entitled Fabric Light Controlled Window Covering Ser. No. 07/701,165 filed May 17, 1991, is disclosed a fabric light control window covering that comprises a first sheer fabric sheet, a second sheer fabric sheet disposed parallel to the first sheet, and a plurality of relatively opaque fabric strips adhesively bonded transversely between the sheet fabrics. Each strip has an edge portion bonded to the first sheet and an opposite edge portion bonded to the second sheet in a manner tending to bias the first and second sheets together. The window covering is movable between a closed position and an open position. The closed position is characterized by a central portion of the fabric strips being substantially parallel to the first and second sheer fabric sheets with the strips themselves being substantially planar. The open position is characterized by the central portion of the fabric strips being substantially perpendicular to the first and second fabric sheets and to the bonded edge portions of the strips themselves. Also, characteristic of this position is that portions of the strips between the bonded edge portions and central portions form smoothly curving surfaces which are free of creases or sharp fold.
The method for manufacturing such a window covering generally includes the following steps. A first line of hot-melt adhesive is applied to the narrow strip material adjacent one edge on one side. A second line of hot-melt adhesive is applied to the narrow strip material adjacent the opposite edge on the opposite side. The narrow strip material is then cut to lengths equal to the width of the wider sheet fabrics and the cut lengths are separated to provide a space between them sufficient to allow for a subsequent processing step. The first sheer fabric is fed at a constant rate longitudinally in a direction perpendicular to the longitudinal direction of the cut strips. The first sheer fabric is also fed over the cut strips in close proximity thereto. As the first sheer fabric is fed, a portion is preheated to a temperature sufficient to form a tack bond with the hot-melt adhesive. Then, while continuously feeding the first sheer fabric at a constant rate, a portion of the first sheer fabric is stopped directly over one of the cut strips so that the cut strip may be pressed and bonded to the first sheer fabric without smearing the adhesive. In order to move the bonded strips out of the way of the next strip, the stopped portion of the first sheer fabric is advanced in machine direction, followed by a backward step to position the first sheer fabric for application of the next cut strip in an overlaying relationship to the previously applied cut strip. The second sheer fabric is then fed into mating contact with the cut strips which have been bonded to the first sheer fabric completing the compilation or collation, thereby forming a sandwich of three layers. Almost immediately after feeding the second sheer fabric, the sandwich or compilation is heated under uniform pressure and tension to melt and force the hot-melt adhesive into the sheer fabrics, and set the layers of the sandwich at a uniform temperature-size relationship. Finally, the fabric sandwich is cooled under uniform pressure and tension, thereby permanently bonding the sheer fabrics to the cut strips without creating warps or wrinkles. All three fabrics are, therefore, heat set and will stay in perfect size relationship to one another. Moreover, the product will be essentially wrinkle-free at any use temperatures. The final, permanently bonded fabric can then be cut to desired lateral widths and/or trimmed along the lateral edges thereof.